Interlock switch



March 7, 1950 D. H. KNOWLTON INTERLOCK SWITCH Filed Dec. 18, 1947INVENTOR. Dar/id h. lfnoa lton BY MM fliforney apparatus.

Patented Mar. 7, 1950 INTERLOCK swrrcn David H. Knowlton, Rockport,Mass, asslgnor to Sylvania Electric Products Inc., a corporation ofMassachusetts Application December 18, 1947, Serial No. 792,388

The present invention relates to switches, more particularly to safetyswitches for high voltage For example, in radio transmitters havingenclosing cabinets it is common to provide a door or removable panelwith a safety switch closed by the panel to complete a power circuitonly when the panel seals the cabinet against hazardous access. Inservicing such equipment it is sometimes desired to knowinglydeliberately connect the power. This entails varied degrees ofdifficulty, depending uponv the design of the safety switch used. When aconventional type of safety switch is deliberately closed with the dooropen the operator may inadvertently disable the safety switchpermanently.

An object of the present invention is to provide a safety switch whichis normally open whenever released, but which is optionally operable forsustained closure under special circumstances. a switch with theautomatic feature that, whenever normally operated to complete thecircuit (as where the cabinet door is closed) the switch will beconditioned to open the circuit when next released. By virtue of thislatter feature assurance is provided that whenever the safety feature isby-passed during testing, the switch will automatically be restored tonormal condition simply by closing the door or panel of the cabinet inwhich the switch is used.

The following is a detailed description of an illustrative embodiment ofa switch for achieving the foregoing objects. In the accompanyingdrawings which show the illustrative switch,

Fig. 1 is an enlarged lateral view thereofwith a side cover-plateremoved,

Fig. 2 is a similar view on a smaller scale of the switch in operativeposition to complete a power circuit when operated by a cabinet closure,

and

Fig. 3 illustrates the same switch as it is to be operatedfor completingthe power circuit where v the cabinet closure is left open.

In Fig. l the switch is provided with a pair of contacts 10 and I2,mounted on leaf springs l4 and I6 and connected to terminals I8 and 20respectively for completing an external circuit. A push button 22 isslidably mounted in the front wall 24 of the switch casing for pressingcontact it against contact l2. The push button is spring-pressed towardthe raised, open-circuit condition by strong leaf spring 26, interposedbetween the push button and leaf spring [4. When such a switch ismounted adjacent a cabinet A further object is to provide such 9 Claims.(Cl. 200 -159) 2 closure, the closure will depress button 22 forcompleting the external circuit.

It is sometimes desired to complete the power circuit of the enclosedequipment without being required to maintain pressure on button 22.

For test purposes it is often desired that the service man should beable to connect the power with the door open, yet have both his handsfree. Forthis purpose the following additional mechanism isincorporated, the effect of which is to by-pass the safety feature ofthe'switch temporarily.

Auxiliary push button 28, also slidable in front wall 24 of the switchcasing, contacts a stiffened extension 30 of leaf spring [4. When button28 is depressed, contact I0 is pressed against con tact l2 whether pushbutton 22 'is operated or not. A latch 32 has a laterally offset portion34 whichllies in the path ofextension 30. Another offset portion 36 oflatch 32 is interposed between button 22 and leaf spring 26. Latch 32has a pivot 38 about which the latch swings in the same directionwhether button 22 or button iii! 28 is depressed.

When button 22 is depressed the switch operates in the normal manner toclose the contacts, and acts incidentally to pivot latch 32 clockwise.pressed latch 32 pivots clockwise until extension 30 passes beyond,portion 34 of the latch, and leaf spring 26 is thereafter effective tosnap extension 34 behind extension 30, thus maintaining the contactsclosed although button 28 may be released." When button 22 alone isdepressed the contacts will remain closed only so long as pressurecontinues to beapplied; but when button 28 has once been depressed thecontacts remain closed although pressure has been released. It ispossible to break connection between contacts l0 and I2 after havingdepressed button 28 by operating button 22. This has the effect ofremoving portion 34 from the return sweep of extension 30. When button22 is depressed and released the switch will be restored to its opencondition. Push button 22 is effective to release the previously latchedcontacts even though button 28 is concurrently operated. Since bothbuttons are arranged to be depressed by a closure the s witch can alwaysbe depended on to be open when the closure is just opened. The serviceman can freely ignore his act of by-passing the safety feature of theswitch after closing the cabinet. Button 22 can also be manuallydepressed during the testing operations to release latch 32 an restorethe open-circuit condition.

Alternatively if button 28 is de- Certaindetailed modifications in theforegoing illustrative embodiment, as well as varied uses of theinvention, will occur to those skilled in the art and I therefore desirethe appended claims to be accorded broad interpretation consistent withthe spirit of the invention.

What I claim is:

1. A electric switch of the class described comprising a pair ofcontacts mutually biased apart, a push button having athrust-transmitting connection to one of said contacts, an auxiliarypush button having a thrust-transmitting connection to one of saidcontacts, both push-buttons being effective when operated to move saidcontacts together, a latch for holding said contacts together when saidauxiliary-push button has been depressed, and a spring acting on saidlatch to move it into the return path of the contact moved by saidauxiliary push button.

2. An electric switch of the class described comprising apair ofcontacts mutually spring-pressed apart, a first push button for pressingsaid contacts together, an auxiliary push button for pressing saidcontacts together, and a latch for holding said contacts together whensaid auxiliary push button has been depressed, said latch having aportion in the line of action of said first push button for moving saidlatch into switch-releasing position.

3. An electric switch of the class described comprising a pair ofcontacts mutually spring-pressed apart, a first push button for pressingsaid contacts together, an auxiliary push button for pressing saidcontacts together, a latch for holding said contacts together when saidauxiliary push button has been depressed, and a spring acting on saidlatch to move it into the return path of the contact moved by saidauxiliary push button, said latch having a portion in the path of actionof said first push button for releasing said contacts.

4. A safety switch comprising a pair of contacts one of which is carriedby an arm and spring-separated from the other contact, a pair ofactuators movable in the same direction for operating said arm andthereby pressing said contacts together, a latch having a portionspring-urged to lie in the path of said arm for holding said contactstogether when so moved by one of said actuators, said latch having aportion operable by the other of said actuators for removing said latchfrom the return path of said arm.

5. A safety switch comprising a pair of contacts one of which isnormally spaced from the other and carried by a leaf spring, a switchcasing having a side wall, a pair of push buttons slidable in said sidewall for moving said leaf spring to close the contacts, a spring-biasedlatch having a portion biased to lie in the return path of said leafspring for maintaining said contacts closed when operated by one of saidpush buttons and having a portion in the path of the other of said pushbuttons for shifting said latch to releas said leaf spring.

6. An electric switch comprising a set of contacts biased towardunoperated condition, a pair of actuators, each actuator having aforce-transmitting connection to said set of contacts and both actuatorsbeing effective individually when operated to establish the sameoperated condition of the contacts, and a latch biased to lock saidcontacts in operated condition upon operation of one of said actuators.

7. An electric switch comprising a set of contacts biased towardunoperated condition, a pair of actuators, each actuator having aforcetransmitting connection to said set of contacts and both actuatorsbeing effective individually when operated to establish the sameoperated condition of the contacts, a latch biased to lock said contactsin operated condition upon operation of one of said actuators, and aforce-transmitting connection between said latch and the other of saidactuators effective to unlock said contacts upon operation of said otherof said actuators in the direction required to establish the operatedcondition of the contacts.

8. A switch comprising a set of contacts normally biased to openposition, actuating means operable in two different motions to closesaid contacts, a latch coacting with said contacts and effective to holdthem closed following one contact-closing motion of said actuatingmeans, and a force-transmitting connection between said actuating meansand said latch effective to operate said latch to contact-releasingposition upon contact-closing operation of said actuating means byanother motion.

9. A switch including a set of normally separated contacts, a first leafspring carrying one of said contacts at an intermediate point, saidspring being fixed at one end and having an extension beyond saidcontact, a second leaf spring fixed at one end to overlie said firstleaf spring and having its free end near said contact, a first pushbutton slidably mounted for travel toward the free end of said secondleaf spring and in the direction to close said contacts, a second pushbutton slidably mounted for travel toward said extension in thedirection to close said contacts, and a pivoted latch having a portionextending between said second leaf spring and said first push buttonwhereby said second leaf spring serves to bias both said latch and saidfirst push button toward unoperated position and said latch is operableagainst that bias by said first push button, said latch having a furtherportion biased to lie in the path of said leaf spring extension, wherebysaid latch is operated by said leaf spring extension to swing out of theforward path of said extension and to snap into the return path of saidextension during depression of said second push button, and to remain inthis configuration until depression of said first push button.

DAVID H. KNOWLTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,214,920 Holland Feb. 6, 19171,234 922 Mattison July 31, 1917 1,912,109 Van Valkenburg et al. May 30,1933

